Production of benzoic acid and like processes



Sept. 3, 1929. D. A. w.,EA|RwEATHER ET AL 1,727,102

PRODUCTION 0F vBENZOIC;ACID AND LIKE PROCESSES Filed New.Y 1e. 192e WUMMHQ H' /NVEN 70H5 Bf. www4@ y Patented Sept. 3, 1929.

isiI STATES DAVID ALEXANDER WHYTE FAIRWEATHER, ERNEST GEORGE BECKETT, AND JOHN THOMAS, OIE' GRANGEMOUT-I, SCOTLAND, ASSIGNORS, BY MESNE ASSIGNMENTS, TO THE SELDEN COMPANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF DELAWARE.

PRODUCTTON OF BENZOIG ACID AND LIKE PROCESSES.

Application filed November 16, 1928, Serial No, 319,952, and in Great Britain September 29,1927.

This invention relatesprincipally to the production of benzoic acid from phthalic acid, but some parts thereof may be applied to like processes, for example, substituted benzoic acid from` substituted phthalic acid, for instance, halogen phthalic acids.

It is well known that phtlialic acid can be converted into benzoic acid by heating calciuin phthalate with calcium hydroxide.

This method is particularly useful when it.

Y is required to produce halogen free benzoic acid, because phthalic acid is easily obtained in a highly pure form Afree from halogens.

In, investigating the manufacture of benzoic acid from the calcium salt of phthalioA acid, we have found that the reaction proceeds y products such as benzene.

smoothly at a temperature of about 1410-450" C. lf, however, an attempt is made to convert any considerable bulk of calcium phthalate into calcium benzoate at this temperature, there is a decided tendency for the reaction to get out of control as a considerable amount of heat is evolved during the conversion, and when this takes places the calcium benzoate formed is decomposed, giving degradation reaction isexotherinic and this is liable to cause decomposition unless measures are taken to prevent the temperatures from becoming too high.

In carrying out the conversion on the large scale itis therefore desirable that only small quantities should be converted at the same time, and the operation is vone which is there- -forle best carried through continuously, with only small quantities. of material at any one time at or near the temperatureof reaction.

The object of the present invention is to provide a process enabling benzoic acid to be produced continuously and on a large scale.

The invention consists in a method for the production of benzoic acid by heating together calcium phthalate and calcium h droxide or like bodies according to which t e temperature of the mass is limited, for exi' (a) By conducting the mixture through a narrow heated tube so that the bulk of the mixture which has arrived at'reaction teinperature is sosmall that the heat evolved is Y suiciently absorbed by the surface of the tube Apparently the so as to prevent the undesirable further decomposition; or

' (b) By using the heat produced by the rei y cor ing to which calcium benzoate or the like is separated from the calcium phthalate or the like which has not undergone the reaction -by using the different solubilities of the above salts in boiling water.

The invention also consists in a process according to either of the preceding two paragraphs carried out so that thebenzoic' acid is obtained from calcium benzoate or the like substantially without loss.v

The invention also consists in methods for the production of benzoic acid substantially as v'hereinafter described. -f

Referringy to the accompanying diagrammatic drawings,

Figure l illustrates an apparatus for carrying the invention into effect in one way according` to the method (a) referred to above,

Figure 2 diagraininaticallyA illustrates one form of apparatus 'for carrying the invention into effect according to the method referred to in paragraph (b) above.

The following examples illustrate how the invention may be carried into effect, all parts being parts vby weight i Example 1.

According to this example the reaction for the'production of benzoic acid is carried through continuously by causing a mixture of calcium phthalate and calcium hydroxide to travel through a heated tube, the rate of conveyance and the temperatures along the tube being so .adjusted that the mixture reachesa maximum temperature of 450 Gg For actube having an internal diameter of three inches, the rate of conveyance of the mixture is about two inches per minute, andy f the tube is maintained at a temperature of 440 C. to 450 C. For smoothness of working it is advisableI to have a'length of the tube not heated so that thereaction mixture .can cool from the reaction temperaturabetube' w ismounted for the greater part of its Example 1 is carried out' in a helical conveyor.. A suitable helical conveyor is shown in We have` found that this decomposition 1sy v itself.

fore it emerges into the air, since we have `:found that if the reaction mixture is allowed immediately to et into contact with the ain I at about 450 o, spontaneous ignition may `take place.

kIn the apparatus shown in Figure l the length in the bath l) but projects beyond they bath to a certain extent at the ends c-and al. At the end 0 a feed hopper e communicates with the interior of the tube by way of the I aperture f. At the end l the .tube a communicates with the receiver g by way of the .opening It. The tube a is heated by means 'of gas' jets z through a suitable alloy or th like 7' contained in the bath l).

Example '2. l

According to this example the process of Figure 1, this comprising the helix 7c mounted on a shaft l driven through gearing m from the driving belt n.

-VVithsuch an apparatus diiicu-lty may be i met by the reaction mixture caking into hard masses which clog the mechanism, TWe have 'found that this difficulty can be overcome bymixing with calcium phthalate and cal-- cium hydroxidel a certain proportion of an mertmaterial which has no influence on the reaction. Such materials are, Jfor example, vcalcium carbonate, sand, ground granite,

or iron in a ne state of' division. We re'- Jfer t o use calcium carbonate because this is obtalned as `a by-product in thereaction MEqmple 3. i *Y This may be regllardedas a modification of Example l, in w perature is used, so as to ensure a small amount of calcium.phthalate remaining in the` mixture at the end of thereaction. Such a temperature may conveniently be, for example, about 435 C. i

- According to this example we arrangethe conditions of the reaction so that no dei composition of calcium benzoate takes place.

probably due toy overheating, and we prefer so to adjust the temperature of the tube that a small proportion of the calcium phthalate is left unacted upon.4 The presence not this remai'ningv calcium phthalate does not appear to be detrimental to the process-as a Whole,

- since we have discovered a method of separating calciumphthalate and/calcium ben- Izoate whichis described below.

Example l..

This is an example, of the treatmentof thev mixture after reaction. i

The crude vrniature whlch emerges from ich a slightly lower tem' the converter tube, and consists of calcium benzoate, possibly some calcium phthalate and calcium carbonate (part of which may be producedby the reaction and part of which maybe present as an inert diluent Amaterial, as described in Example 2) is boiled with suiiicient water to dissolve the calcium benzoate (that is, at least 10 times 'the weight of calcium benzoatc present in the mixture),- The boiling mass isfiltered hot and the residue in the press consists oit' calcium carbonate and unchanged calcium phthalate. ,The filtrate is acidified, preferably at the boiling point, with sulphuric acid and the calcium sulphate filtered off.

The benzoic acid crystallizes `out on cooling and the mother liquors are used for extracting the next batch; by this last step we ensure that the small amount of benzoic acid that remains dissolved in the mother liquor is not lost.

The ilterpress residues, consisting of calcium carbonate and any unchanged calcium phthalate that may be present, are' treated witlrphthalic acid orphthalic anhydride so as to convert part of the calcium carbonateinto calcium phthalate. It is then mixed with limc and filtered. The press cake is dried and ground and is ready for sending through the converter tube.

Example 5.

According to this example the following substances are used in the proportions stated namely* g Parts. Calcium phthalate 400 vCalcium hydroxide (4 Calcium carbonate 480 'This mixture is sent through the converter as indicated above.

Generell.l

Whilst the main object of the present invention is to deal with theemployment ot phythalic acid for the production of benzolic A suitable apparatus vin which the heat l produced by the reaction of one part of the mixture to bring the temperature of `adjacent parts -to a reaction point is shown in Figure 2. This apparatus includes the coniso tainer or drum o mounted in bearings p and adapted to be driven from the driving belt g. The drum is heated by the agency of gas jets 7* and gaseous products passed to the atmos-` phere from the inside of the drum 0 byway of the fixed pipe s. lVhcn employing` the apparatus shown in Figure 2, the container is rotated while the mixture is being brought to about 420 C. Rotation is then stopped during the initiation and course of the rcaction,

We have found that the conversion of fairly large quantities can be .carried through if the temperature of the mixture of calcium hydroxide and calcium phthalate is broughtup to about 420 C., that is near ly to the temperature at which the reaction proceeds with rapidity, and if then the source of heat is withdrawn from the main mass and a small portion is heated tobetween 4404500 C. the reaction then starts and will extend throughout the whole mass without attaining a temperature which causes decomposition ofthe calcium ben Zoate to any material extent. The reaction mass in this case can be worked and benzoic acid separated from it by the method outlined above. The 'conversion of the calcium phthalate in bulk can also be carried out in the presence of calcium carbonate or other inert material.

The invention is not limited to the use of calcium salts. The method of conversion and working up may also be `carried out With the other alkaline earth salts.

Having now described Aour invention, what we claim as new and desire to secure by Letters Patent is 1. A method which consists in conducting a reactingmixture containing at least one solid constituent through a narrow heated tube, so that the bulk of the mixture, which has arrived at reaction telnperature, is so small that the heat evolved s suiiciently absorbed by the surface of the tube so as to prevent undesirable .decomposition.

2. A method of bringing about exothermic reactions including organic compounds which comprises conducting a reaction mixture at least one of the components being a solid through a narrow heated tube so that the bulk'of'the mixture which has arrived at reaction temperature is so small that the heat evolved is suiiciently absorbed by the surface of the tube so as to prevent .undesirable'decomposition or side reactions.

3. A method of transforming polycarboxylic acid compounds into monocarboxylic acid compounds which comprises conducting a reaction mixture containing the polycarboxylic acid compounds through a narrow heated tube, at least one constituent of the reaction mixture being a solid so that the bulk of the mixture which has arrived at reaction temperature is so small that any heat evolved is sufficiently absorbed by the surface of the tube so as to prevent undesired decomposition or side reactions.

4. A method according to claim 3 in which the reaction mixture contains at least one salt of the polycarboxylie acid compound.

5. A method according to claim 3 in which the reaction mixture contains at least one salt of the polycarboxylic acid compound and at least one alkaline hydroxide.

6. A method of producing a benzoic acid compound which comprises conducting a reaction mixture containing a salt of phthalic acid through a narrow heated tube at least one constituent of the reaction mixture being a solid so that the bulk of the mixture which has arrived at reaction temperature is lso small that the heat evolved is suii-l ciently absorbed by the surface of the tube so as to prevent undesirable decomposition.

7. A method according to claim 6 in which the reaction mixture contains calcium phthalate and calcium hydroxide.

8. A method according to claim 1 in which the reacting mixture contains solid diluents.

9. A lmethod according to claim 2 in which the reacting mixture contains solid diluents.

10. A method according to claim 3 in which the reacting mixture contains solid diluents.

11. A method according to claim 6 in which a solid diluent is present in the reaction mixture.

12. A method according to claim 6 in which the reaction mixture contains an' alkaline earth metal phthalate, an alkaline earth metal hydroxide and a solid diluent.

13. A method according to claim 6 in' lcarbonate.

In testimony whereof we have signed our names to this specification.

DAVID ALEXANDER WHYTE FAIRWEATHER.

ERNEST GEORGE BECKETT.

JOHN THOMAS. 

